Method and apparatus for determination of coagulant injection rate in water treatment process

ABSTRACT

Provided are a method and an apparatus that enable rapid and automatic determination of the coagulant injection rate in a process of water treatment through coagulation and sedimentation. Using a coagulation analyzer comprising sample tanks  1 A to  1 D each for keeping a predetermined amount of raw water, a water supply pump  7 , water supply/discharge valves  4, 6  for raw water and washing water, mixers  3 A to  3 D, a coagulant injection unit  21 , and a detector  30  for determining the particle size and the particle number of flocs, the time within which the coagulant  20  injected into the sample tanks is dispersed by mixing and the particles begin to agglomerate (agglomeration start time) is determined, and based on the thus-determined agglomeration start time, the coagulant injection rate is determined, or the amount of the coagulant to be injected is controlled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and an apparatus fordetermination of the coagulant injection rate (ratio of the amount ofcoagulant to be injected to the amount of water to be treated) incoagulation and sedimentation for treating surface running water such asriver water, lake and marsh water, or industrial water, sewage, sludge,factory wastes, etc.

2. Background Art

A water purification plant employing a rapid filtration system generallycomprises a mixing basin for rapid mixing with coagulant injectionthereinto, a flocculation basin for growing the flocs formed in themixing basin, a sedimentation basin for sedimenting and removing thegrown flocs, and a filtration basin for removing the particles and flocsthat could not be sedimented in the previous step (see FIG. 7 in PatentReference 2).

The important point in the rapid filtration system is that the coagulantinjection rate therein is controlled at a proper level in accordancewith the quality of the raw water to be treated (untreated water),thereby forming well-sedimentable flocs. Coagulation treatment, ifeffected at an unsuitable coagulant injection rate, gives problems ofloss head increase in filtration basin, backwash frequency increase, andoutflow of particles from filtration basin, owing to carryover of flocsfrom sedimentation basin or coagulation failure.

A suitable coagulant injection rate varies depending on not only theturbidity of raw water but also the alkali degree, the pH and thetemperature thereof, and therefore differs for different raw water; andaccordingly, it is impossible to indiscriminately determine thecoagulant injection rate on the basis of the raw water turbidity.Heretofore, therefore, the following methods have been employed in waterpurification plants for monitoring the coagulation condition anddetermining and controlling the coagulant injection rate.

(1) Jar Test:

The process is as follows: A constant amount of raw water to be treatedis sampled in some beakers, the coagulant injection rate is stepwisevaried in every beaker, the water in each beaker is coagulated throughrapid mixing and slow mixing, then this is statically kept for apredetermined period of time, and thereafter the turbidity of thesupernatant and the flocs sedimentation condition in each beaker arechecked, thereby determining the coagulant injection rate (see FIG. 8 inPatent Reference 2).

These steps in the process are generally carried out by manual analyticoperation; however, as in Patent Reference 1, an auto-jar tester hasbeen put into practical use, which is for full-automatically attainingall the steps of raw water sampling, coagulant injection, determinationof mixer rotation number and rotation time, and supernatant turbiditymeasurement (for its details, see Patent Reference 1).

(2) Injection Rate Formula:

This is for feed-forward control based on the injection rate formulathat indicates the relation to a suitable coagulant injection rate withparameters of the turbidity, the pH, the alkali degree and thetemperature of raw water. The injection rate is found according to anexperimental method based on a jar test and on the turbidity of theprecipitated water in actual plants. As an advanced modification of thissystem, there are known a technique of feedback control combinationbased on the measured value of precipitated water turbidity, and atechnique of utilizing fuzzy and neuro control for approximation tooperators' jar test results and running results in actual plants (seeparagraphs [0006] and [0007] in Patent Reference 2).

(3) Coagulation Sensor:

This is a method for controlling the coagulant injection rate, in whichlight beams are applied to the flow of the fluid to be analyzed, and themean particle size and the particle concentration of the flocs areobtained from the mean value of the transmitted light amount and thestandard deviation thereof, and the coagulant injection rate is therebycontrolled so that the mean particle size of the flocs could be on asuitable level, like the method of the invention disclosed in PatentReference 2 (for its details, see Patent Reference 2).

The following Patent References 3 to 6 that disclose the techniquesrelating to the present invention are described below for convenience ofexplanation thereof.

Patent Reference 1: JP-A 2-114178

Patent Reference 2: Japanese Patent No. 3205450

Patent Reference 3: Japanese Patent No. 3672158 (corresponding to U.S.Pat. No. 6,184,983)

Patent Reference 4: Japanese Patent No. 2824164

Patent Reference 5: JP-A 10-311784 (laid-open publication of PatentReference 3, corresponding to U.S. Ser. No. 09/037,431)

Patent Reference 6: JP-A 2002-90284

However, the coagulation condition confirmation method and the coagulantinjection rate determination method described in the above have thefollowing problems.

The jar test method of (1) requires operators well skilled in the art,and has a problem in that it may give different data depending ondifferent operators. In addition, it takes a long time of 30 minutes orso for confirming the coagulation condition and for determining areasonable coagulant injection rate; and therefore, it is difficult tofrequently carry out the jar test, and the method is problematic in thatthe reflection of its data on the coagulant injection rate in actualplants may be delayed.

Use of an auto-jar tester for automation of jar test operation maygreatly reduce the load of operators' work; however, the method stilltakes 30 minutes or so for obtaining the test data, and therefore couldnot solve the problem of long time lag.

In the method based on the injection rate formula of (2), the injectionrate formula differs for different raw water, and therefore, the methodrequires injection rate formula control in every water purificationplant. In addition, in this, there is not the guarantee of permanentusability of the injection rate formula. Specifically, when a dam isconstructed on the upstream side of a water intake port, or when riverbank construction works are made, or owing to the influence of a heavyrain, the relation between the quality of water and the optimumcoagulant injection rate may be broken, and therefore the method has aproblem in that it lacks site and time universality.

The method with a coagulation sensor of (3) enables real-time automaticcontrol of a coagulant injection rate to give flocs having a suitablefloc particle size, and this solves the operator problem and thetime-lag problem in (1) and solves the universality problem in (2).However, the suitable floc particle size differs depending on thequality of raw water, and therefore, for automatic control of coagulantinjection, a database must be previously formed for the relation betweenthe raw water turbidity and the optimum floc particle size.Specifically, data with a coagulation sensor must be obtained throughthe four seasons, and the method is problematic in that it takes a lotof time before its practical use.

In the above, there are mentioned various problems in water purificationplants; and needless-to-say, coagulation and sedimentation in treatingindustrial water, sewage and factory wastes also has similar problems.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-mentioned problems, and an object of the invention is to provide amethod and an apparatus for determination of a coagulant injection ratein water treatment through coagulation and sedimentation, which enableautomatic determination of a reasonable coagulant injection rate withina short period of time.

To solve the above problems, the invention is a method of determiningthe ratio of the amount of coagulant to be injected to the amount ofwater to be treated (coagulant injection rate) in a process of watertreatment through coagulant injection to water to be treated followed bycoagulation and sedimentation, which comprises the following steps(claim 1):

(1) A step of collecting a predetermined same amount of the water to betreated in every one of plural sample tanks, and then injecting apredetermined different amount of a coagulant to each water samplecollected in those sample tanks, thereby preparing water samples eachhaving a different coagulant injection rate (coagulant injection step);

(2) A step of individually mixing, after the coagulant injectionthereto, every water sample to thereby disperse the coagulant therein,and individually determining the time taken before the start ofagglomeration of the particles in each water sample (agglomeration starttime) for every water sample (agglomeration start time determinationstep);

(3) A step of computing, based on the agglomeration start timedetermined for every water sample and on the coagulant injection ratefor them, the correlation between the agglomeration start time and thecoagulant injection rate, as a fitting line (fitting line computingstep);

(4) A step of computing, based on the reasonable agglomeration starttime data previously set for a water treatment plant and on the abovefitting line, a reasonable coagulant injection rate for the watertreatment plant (reasonable coagulant injection rate computing step).

In the invention of the above claim 1, plural sample tanks are used;however, as in the invention of the following claim 2, one sample tankmay be used repeatedly thereby determining the agglomeration start timefor water samples having a different coagulant injection rate.Specifically, of the coagulant injection rate determination method ofthe above claim 1, the modification comprises the following steps (1a)(2a) and (2b) in place of the above steps (1) and (2) (claim 2).

(1a) A step of collecting a predetermined amount of water to be treatedin one sample tank, then injecting a predetermined amount of a coagulantto the water sample collected in the above sample tank, and after thecoagulant injection, dispersing the coagulant by mixing, and determiningthe time taken before the start of agglomeration of the particles in thewater sample (agglomeration start time);

(2a) After the above step, a step of washing the sample tank withwashing water, then removing the washing water from the sample tank,then again collecting a predetermined amount of the water to be treatedin the sample tank, and injecting a predetermined amount, which differsfrom that in the above step, of the coagulant into the water sample, anddetermining the agglomeration start time for the water sample;

(2b) A step of repeating the operation of the above step plural timeswith varying the coagulant injection amount every time, and determiningthe agglomeration start time for every water sample each having adifferent coagulant injection rate.

Further as in the invention of the following claim 3, in case where adatabase of a relational formula and the like previously obtainedthrough experiments relative to the correlation between theagglomeration start time and the coagulant injection rate is used, thena reasonable coagulant injection rate may be computed by using onesample tank and by determining the agglomeration start time for onewater sample in the tank. Specifically, the method is for determiningthe ratio of the coagulant injection amount to the amount of water to betreated (coagulant injection rate) in a process of water treatmentthrough coagulant injection to water to be treated followed bycoagulation and sedimentation, and this comprises the following steps(claim 3):

(1) A step of collecting a predetermined amount of the water to betreated in one sample tank, then injecting a certain amount, which ispredetermined on the basis of the quality of the water to be treated, ofa coagulant to the water sample collected in the sample tank, and afterthe coagulant injection thereto, mixing it to thereby disperse thecoagulant therein, and determining the time taken before the start ofagglomeration of the particles in the water sample (agglomeration starttime);

(2) When the difference between the measured value of the agglomerationstart time as determined in the above and the reasonable value of theagglomeration start time as previously set in accordance with a watertreatment plant falls within a predetermined range, a step ofdetermining the coagulant injection rate corresponding to thepredetermined amount of the coagulant in the above step (1), as thereasonable coagulant injection rate; but when the above difference islarger than the predetermined range, a step of computing the reasonablecoagulant injection rate according to the following process of (21) to(23):

(21) The correlation between the agglomeration start time and thecoagulant injection rate is defined by a general formula including twoconstants, then based on the database previously obtained throughexperiments, one of those constants is defined based on the quality ofthe water to be treated, and the general formula including one constantis found;

(22) Based on the general Formula including one constant and on themeasured value of the agglomeration start time and the coagulantinjection rate at that time, the other constant is found, whereby thecomputational formula for the correlation between the agglomerationstart time and the coagulant injection rate is specifically defined;

(23) Based on the specifically-defined computational formula and thereasonable value of the agglomeration start time as previously set inaccordance with the water treatment plant, the reasonable coagulantinjection rate is computed.

As embodiments of the invention of the above claim 1 or 3, preferred arethose of the following claims 4 to 6. Specifically, one preferredembodiment of the coagulant injection rate determination method of theabove claim 1 or 3 is as follows: In the method, the number of theparticles in the water sample is counted in their respective particlesize sections, and the agglomeration start time is specifically definedby at least any one time of a particle number decrease start time thatis determined for the particles previously existing in the water samplebefore the coagulant injection thereinto and falling in predeterminedsmall particle size sections, or a particle number increase start timethat is determined owing to the start of agglomeration after thecoagulant injection for the particles in the predetermined largeparticle size sections larger than those in the above predeterminedsmall particle size sections (claim 4).

Another preferred embodiment of the coagulant injection ratedetermination method of the above claim 1 or 3 is as follows: In themethod, the mean particle size and the number of the particles in awater sample are determined, the time at which the mean particle sizebegins to increase is counted as a floc growth start time, and the pointat which the mean particle number to be counted as the number of flocsbegins to increase is defined as a floc number increase start time, andthe agglomeration start time is specifically defined by at least any onetime of the floc growth start time or the floc number increase starttime (claim 5).

Still another preferred embodiment of the coagulant injection ratedetermination method of the above claim 1 or 3 is as follows: In themethod, the reasonable value of the agglomeration start time to bepreviously set in accordance with a water treatment plant is one to beset on the basis of the residence time of the water to be treated in themixing basin provided in the water treatment plant (claim 6).

The residence time of the water to be treated in the mixing basin isdetermined by the volume of the mixing basin and the amount of the waterto be processed in the actual water treatment plant (actual plant). Thereasonable coagulant injection rate in the actual plant varies everymoment depending on the quality of the water to be treated (raw water),and therefore, the water to be treated must be suitably collected in asample tank and the reasonable coagulant injection rate must bedetermined in accordance with the change.

Further, as an invention relating to an apparatus for determination ofthe coagulant injection rate, preferred is the invention of thefollowing claim 7. Specifically, this is an apparatus for carrying outthe coagulant injection rate determination method of the above claim 1or 3, and comprises at least one sample tank equipped with a mixer, acoagulant injection device for injecting a predetermined differentamount of a coagulant, an agglomeration start time counter, and acomputer device for computing a reasonable coagulant injection rate(claim 7).

The present invention makes it possible to automatically determine areasonable coagulant injection rate within a shorter period of time thanin conventional methods, in a process of water treatment throughcoagulation and sedimentation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an essential flowchart of Example 1, in which a coagulationanalyzer, as an apparatus for carrying out the coagulant injection ratedetermination method of the invention, is connected to a waterpurification process flowchart.

FIG. 2 is a schematic constitutional view of Example 1, showing thecoagulation analyzer of FIG. 1.

FIG. 3 is a schematic, side cross-sectional view of the sample tank inFIG. 2.

FIG. 4 is a graph showing the profile of the particle number countedafter coagulant injection into water samples.

FIG. 5 is a graph showing one example of the test data relating to theprofile of the particle number of 1 to 3-μm particles, for explanationof agglomeration start time.

FIG. 6 is a graph showing one example of the test data relating to theprofile of the particle number of 3 to 7-μm particles, for explanationof agglomeration start time.

FIG. 7 is a graph showing the fitting line as a correlation betweenagglomeration start time and coagulant injection rate.

FIG. 8 is a comparative explanatory view showing a conventional methodand a method of the invention of Example 1, relative to the time to betaken for determination of coagulant injection rate in those methods.

FIG. 9 is a schematic constitutional view of Example 2 that differs fromFIG. 2, showing the coagulation analyzer of FIG. 1.

FIG. 10 is a graph showing the profile of the mean particle size asmeasured after coagulant injection into water sample, relative to flocgrowth start time.

FIG. 11 is a graph showing the profile of the mean particle number offlocs as measured after coagulant injection into water sample, relativeto floc number increase start time.

FIG. 12 is a graph showing the relation between the measured value andreasonable value of agglomeration start time, the general formula ofcoagulant injection rate and agglomeration start time, and the Injectionratio computation formula after determination of constants, in Example2.

In these drawings, 1, 1A to 1D are a sample tank; 3, 3A to 3D are amixer; 4 is a raw water intake valve; 5 is a raw water discharge valve;6 is a tap water intake valve; 7 is a water supply pump; 10 is a rawwater feed valve; 11 is a water discharge valve; 12 is a overflow wall;14 is a water level control tank; 20 is a coagulant; 21 is a coagulantinjection unit; 22 is a coagulant injector tube; 23 is an injector tubeoperator; 24 is a stage; 30 is a detector for measuring the particlesize of flocs and counting the particle number thereof; 31, 31A to 31Dare a water intake tube; 32, 32A to 32D are a water intake pump; 33 isan electric signal from detector; 34 is a sequencer for analyzing theelectric signal from detector and for device control; 35 is a POD fordisplaying the measured value and for inputting the condition data indevice setting.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are described with reference to FIG. 1; andtheir details are described in the section of Examples. The inventionshould not be restricted by the description of the following embodimentsand Examples.

In general, in coagulation and sedimentation treatment, particlesagglomerate and grow into flocs in a process from rapid mixing in amixing basin after injection of a coagulant thereinto to slow mixing ina flocculation basin, as in FIG. 1. In this stage, it is fundamentalthat the agglomeration begins in the mixing basin, and it is importantthat the agglomeration start time is on the same level as that of theresidence time in the mixing basin.

In this situation, the treatment after the mixing basin may be attainedfavorably, thereby giving well-sedimentable flocs and reducing theturbidity of the precipitated water. In this, the agglomeration starttime is influenced by the quality such as the turbidity, the alkalidegree, the pH and the temperature of raw water, and also by the mixingintensity and the coagulant injection rate; and of those, the coagulantinjection rate may be readily controlled in actual plants. Specifically,when the coagulant injection rate is lower than a reasonable level, thenthe agglomeration start time may be longer than the residence time inthe mixing basin, thereby causing problems in the subsequentflocculation. On the other hand, when the coagulant injection rate ishigher than a reasonable level, then the agglomeration start time may beshorter than the residence time in the mixing basin, and the coagulantis under situation of over-injection. In the present invention, a partof the water to be treated (raw water) is led to run into a coagulationanalyzer shown in FIG. 1, and in this coagulation analyzer, thecoagulant injection rate is controlled so that the agglomeration starttime could be a predetermined value for the water quality that variesevery moment, whereby the same results as those in evaluation of thefloc sedimentation performance and the supernatant turbidity in a jartest and those in optimum floc particle size control with a coagulationsensor could be obtained.

Specifically, in the coagulation analyzer, when the agglomeration starttime is determined and the coagulant injection rate is controlled inaccordance with the time, then the method does not require a step ofstatically keeping the system after the slow mixing step, and thereforethe coagulant injection rate may be automatically determined withinabout 10 minutes or so. Accordingly, the operation by some skilledoperators as in the jar test may be omitted, and further, coagulantinjection rate control taking a shorter time lag than that with anauto-jar tester may be realized. In addition, since the method does notrequire a database of raw water turbidity and reasonable floc particlesize distribution which, however, is required by a coagulation sensor,the coagulant injection rate control system with the coagulationanalyzer is characterized in that it may be driven for practical usewithin a relative short period of time after the apparatus installation.

Next described are concrete methods of determination of theagglomeration start time and determination and control of the coagulantinjection rate, using a coagulation analyzer.

For determination of the agglomeration start time in the invention,employed is at least any one of the following two methods. The firstmethod is a particle counting method, and this is the same as the methoddisclosed in Patent Reference 3. The particle counting method is asfollows: A water sample running in a detector is irradiated with lightbeams, and at least one light of the front scattering light, the sidescattering light, the back scattering light and the transmitted light isreceived by a photoelectric converter, and from the number of theelectric signal pulses converted in the photoelectric converter within apredetermined period of time and the height of each pulse, the number ofthe particles is counted in their respective particle size sections. Inthe first method of the invention, for the particles falling within theparticle size sections in which the number of the particles is large,the time at which the number of the particles begins to decrease fromthe coagulant addition start time is referred to as a particle numberdecrease start time; and for the particles falling within the particlesize sections in which the number of the particles is small, the pointat which the number of the particles begins to increase is referred toas a particle number increase start time; and at least any one or bothof the particle number decrease start time and the particle numberincrease start time are employed for specifically defining theagglomeration start time.

The second method is a fluctuation analyzing method, and this is thesame as the method disclosed in Patent Reference 4. The fluctuationanalyzing method is as follows: A water sample running in a detector isirradiated with light beams from at least one site, and at least onelight of the front scattering light, the side scattering light, the backscattering light and the transmitted light is received by aphotoelectric converter, and from the mean value and the standarddeviation of the electric signals converted and outputted from thephotoelectric converter within a predetermined period of time, the meanparticle size and the number of the particles contained in the watersample are found. In the second method of the invention the time atwhich the mean particle size begins to increase from the coagulantaddition start time is referred to as a floc growth start time; and thetime at which the number of the particles to be counted as flocs beginsto increase from the coagulant addition start time is referred to as afloc increase start time; and at least any one or both of the flocgrowth start time and the floc increase start time are employed forspecifically defining the agglomeration start time.

The method of finding the mean particle size and the particle numberfrom the mean value and the standard deviation of the electric signalsis described in Patent Reference 4. As a modification of the patentmethod, there is known a method of controlling the coagulant injectionrate so that the floc mean particle size could be on a reasonable level,like the method described in Patent Reference 2. However, these differfrom the present invention in the following points. First, in themethods described in Patent Reference 4 and Patent Reference 2, acoagulant is injected continuously, and therefore, the suspensoidparticles before coagulation exist along with flocs in various growthstages. Accordingly, in the methods described in Patent Reference 4 andPatent Reference 2, it is impossible to determine the time at which thenumber of particles begins to decrease through agglomeration ofparticles, the time at which the particle size of flocs begins toincrease with the start of the growth of flocs, and the time at whichthe number of blocs begins to increase (agglomeration start time),which, however, are determined in the present invention. As a result, inthe methods described in Patent Reference 4 and Patent Reference 2, itis impossible to realize controlling the coagulant injection rate basedon the agglomeration start time as in the present invention. To thateffect, it should be said that the method of the present inventiondiffers from the methods of the inventions of Patent Reference 4 andPatent Reference 2.

The device with which the agglomeration start time and the number andthe mean particle size of flocs are determined according to theabove-mentioned first or second method of the present invention isreferred to as a coagulation analyzer.

As the method of controlling a coagulant injection rate in theinvention, employed is any of the following methods. The first method isas follows: In a coagulation analyzer, an agglomeration start time isdetermined at a different coagulant injection rate, and from themeasured value, a relational formula of the agglomeration start time andthe coagulant injection rate is derived, and thereafter a set value of apredetermined reasonable agglomeration start time is given to therelational formula, thereby finding the optimum coagulant injectionrate.

The second method is as follows: In an injection rate formula having atlest one index of the turbidity, the alkali degree, the pH and thetemperature of raw water, as a Parameter, a coagulant injection ratethat may be expected to be reasonable is previously found, and in casewhere the agglomeration start time at that injection rate is determinedwith a coagulation analyzer, and when the agglomeration start time fallsoutside a predetermined time range, then from the relational formula ofthe predetermined agglomeration start time and the coagulant injectionrate, the correction value of the coagulant injection rate is found forcorrecting the agglomeration start time to fall within the predeterminedtime range.

EXAMPLES Example 1

As in FIG. 1, the coagulation analyzer in the invention is disposed in awater purification system where raw water taken from a river is fed intoa water well, then led to a rapid mixing basin in which it is rapidlymixed with a coagulant injected thereinto, and then the agglomeratesformed in the rapid mixing basin are grown into flocs in a flocculationbasin, then the resulting flocs are sedimented in a sedimentation basin,and the supernatant is filtered in a filtration basin, in such a mannerthat the analyzer is branched from the line from the water well in thesystem. As the case may be, the coagulation analyzer may be connected toa raw water line through which raw water is fed to a quality test roomfor the purpose of carrying out a jar test or for inspection of thequality of raw water.

In this, the present invention is characterized in that the reasonablecoagulant injection rate, as determined from the agglomeration starttime found in the coagulation analyzer, is reflected on the coagulantinjection rate in the water purification process.

The coagulation analyzer in Example 1 comprises, as in FIG. 2, aplurality of (4 in this Example) sample tanks 1A to 1D for keeping apredetermined amount of raw water, water supply/discharge valves 2A to2E, mixers 3A to 3D, a raw water intake valve 4, a raw water dischargevalve 5, a tap water intake value 6, a water supply pump 7, a filter 8,a filter inlet valve 9, a raw water feed valve 10, a water dischargevalve 11, a water level control tank 14 connected with a duct 13 fordischarging the water overflowing from the overflow wall 12, a coagulant20, a coagulant injection unit 21, a coagulant injector tube 22, aninjector tube operator 23, a stage 24, a detector 30 for measuring theparticle size of flocs and counting the particle number thereof, waterintake tubes 31A to 31D, water intake pumps 32A to 32D, a sequencer 34for analyzing the electric signal 33 from detector and for devicecontrol, and a POD (programmable operation display) 35 for displayingmeasured value and for inputting condition data in device setting.

In this, the detector 30 comprises, as disclosed in Patent Reference 3,a light beam radiation unit comprising any of a laser, LED or lamp forradiating light beams toward a water sample, a photoelectric converterthat receives at least any one light of the front scattering light, theside scattering light, the back scattering light or the transmittedlight generated by the particles contained in a water sample, andconverts it into an electric signal, and an electric circuit that countsthe number of the particles in their respective particle size sectionsfrom the number of the converted electric signal pulses and the heightof the pulses.

As a concrete method of measuring the particle size and counting thenumber of particles, there are known the method described in PatentReference 5 for counting the number of the particles in a water sample,as an example of using a semiconductor laser as the light radiation unitand using an optical system of receiving front scattering light, and themethod described in Patent Reference 6 as an example of using asemiconductor laser as the light radiation unit and using an opticalsystem of receiving transmitted light. In this Example, the detector 30is driven according to the abovementioned particle counting method;however, in place of it, the optical system according to a fluctuationanalyzing method as in Patent Reference 4 may also be employed.

Next described is a concrete process of the method for determining theagglomeration start time.

First, for discharging the water sample remaining in the sample tanks 1Ato 1D, the mixers 3A to 3D, the water supply pump 7, and the waterintake pumps 32A to 32D are stopped; the raw water discharge valve 5 isopened; the raw water intake valve 4, the tap water intake valve 6, thefilter inlet valve 9, and the raw water feed valve 10 are shut; and thewater supply/discharge valves 2A to 2E, and the water discharge valve 11are opened (this is hereinafter referred to as a water sample dischargestep).

After the water sample is discharged out of the sample tanks 1A to 1D,the tap water intake valve 6 and the filter inlet valve 9 are opened,and tap water is fed into the system by the water supply pump 7 via thetap water intake valve 6; and via the filter inlet valve 9, the waterpasses through the filter 8 by which particles are removed (hereinafter,this is referred to as washing water). The washing water is then fedinto the sample tanks 1A to 1D and the water level control tank 14 viathe water supply/discharge valves 2A to 2E. The water discharge valve 11is shut, whereby the sample tanks are gradually filled with the washingwater; and as in FIG. 3 showing the side view of the sample tank, thewater having overflowed from the sample tank is discharged via the ducts15A to 15D (only 15A is shown) (hereinafter this is referred to as awashing water Feed step).

In this, the height of the overflow must be higher than the water leveldefined by the height of the overflow wall 12. In case where a flowmeter 16 having a flow switch or an output function is disposed in thesystem, then the situation where the sample tanks are filled with watercould be automatically detected. In this step, when the mixers 3A to 3Dare kept working to wash the sample tanks, then it is effective intreatment of raw water having high turbidity and chromaticity.

After the washing water feed step, or that is, after the washing wateris fully fed to the sample tanks, the water intake pumps 32A to 32D aredriven, and the washing water is analyzed with the detector 30. In thisstep, when the voltage level as measured in the photoelectric converter,and the information of the particle size and the particle number to beobtained through conversion of the number and the height of the pulsesgenerated when the particles run through the light beams are kept inmemory, then the contamination of the optical system and thedeterioration of the filter may be confirmed and further the quantity oflight may be corrected (hereinafter this is referred to as a zero waterdetermination step).

After the zero water determination step, the discharge valve 11 isopened, the water supply pump 7 is stopped, the filter inlet valve 9,the raw water feed valve 10 and the tap water intake valve 6 are shut,and the washing water in the sample tanks and the water level controltank are discharged (hereinafter this is referred to as a washing waterdischarge step); and then the raw water intake valve 4 and the raw waterfeed valve 10 are opened, the raw water discharge valve 5 is shut, thewater supply pump 7 is driven, the water discharge valve 11 is shut, andthe water supply/discharge valves 2A to 2E are opened (hereinafter thisis referred to as a raw water feed step).

After the sample tanks are filled with raw water, or that is, after apredetermined period of time or after the flow meter 16 having a flowswitch or an output function detects each sample tank filled with rawwater, then the water supply pump 7 is stopped, the raw water feed valve10 and the raw water intake valve 4 are shut, and the raw waterdischarge valve 5 is opened. With that, the water level in each sampletank reaches the height of the overflow wall 12 in the water levelcontrol tank 14, and the water sample of the same capacity may bedefined in every test. Then, the water supply/discharge valves 2A to 2Dare shut (hereinafter this is referred to as a water level controlstep).

In this, for the overflow wall 12, a material having a different heightmay be used in different cases, thereby changing the capacity of thewater sample.

After the water level is controlled, the mixers 3A to 3D are driven at apredetermined revolution speed. Next, the water intake pumps 32A to 32Dare driven, the number of the particles in raw water or the turbidity ofraw water is determined with the detector 30; and based on the measuredvalue, the range of the coagulant injection rate in each of the sampletanks 1A to 1D is determined. In this step, the discharge water from thewater intake pumps 32A to 32D may be returned back to the sample tanks.After the raw water is assayed for a predetermined period of time, acoagulant 20 is injected into the sample tanks 1A to 1D in that orderfrom a coagulant injection unit 21 that comprises a metering pump or asyringe pump. In this, the coagulant injection tube 22 is connected tothe injection tube operator 23 and moves on the stage 24, whereby acertain amount of a coagulant that is determined through the abovemeasurement is injected into each sample tank (hereinafter this isreferred to as a coagulant Injection step).

After the coagulant is injected, it is dispersed by mixing to startagglomeration of particles. FIG. 4 shows the profile of the particlenumber counted with the detector 30 in this step. Specifically, the rawwater tested in this Example contained a lot of particles having aparticle size of from 1 to 3 μm, the particles were counted with thedetector 30 before the coagulant injection; but in about 3 minutes afterthe coagulant injection, the agglomeration began, and the number of theparticles having a particle size of from 1 to 3 μm began to decrease.Afterwards, the number of particles having a particle size of from 3 to7 μm, which did not almost exist before the coagulant injection, beganto increase. This shows the agglomeration of particles to formmicroflocs. After further lapse of time, the microflocs grew largerflocs, and therefore the number of the particles having a particle sizeof from 3 to 7 μm began to decrease and at the same time, the number ofparticles falling within a particle size section of from 7 to 10 μm, andthose within a section of from 10 to 15 μm began to gradually increase.

In this apparatus, the number and the particle size of the particlesthat are predominantly present in the raw water to be treated may beselected and determined in any desired manner; and the suitable particlesize of the particles that may be in the raw water treated in thisExample is from 1 to 3 μm. In this, the time at which the number ofparticles begins to decrease is defined as a particle number decreasestart time, as in FIG. 5. In this apparatus, the particle number isoutputted and led into the sequencer 34 from the detector via theelectric signal 33, and the particle number decrease start time isconfirmed in the sequencer and kept in memory. On the other hand, thenumber and the particle size of the particles not so much existing inthe raw water may also be selected and determined in any desired manner;and in this Example, the particle size of the particles is suitably from3 to 7 μm. In this, the time at which the number of particles begins toincrease is defined as a particle number increase start time, as in FIG.6; and the time is kept in memory in the sequencer (hereinafter this isreferred to as an agglomeration start time determination step).

Either one of the particle number decrease start time or the particlenumber increase start time is taken as the agglomeration start time; orthe mean value of both the two is taken as the agglomeration start time;and this may be previously determined, and any of these may be employedherein.

When the agglomeration start time in each sample tank is determined,then the relation between the coagulant injection rate and theagglomeration start time in each of A to D may be plotted, as in FIG. 7.The coagulation analyzer in the invention is to find the relationalformula (fitting line) between the coagulant injection rate and theagglomeration start time through polygonal line approximation or leastsquare approximation to multinomial expression with these data(hereinafter this is referred to as a fitting line computation step).

Next, the agglomeration start time previously set as a reasonable valuein a water treatment plant is given to the above-mentioned relationalformula, thereby computing a suitable coagulant injection rate (this ishereinafter referred to as a reasonable coagulant injection ratecomputation step).

The reasonable value of the agglomeration start time may be determinedon the basis of the residence time in a mixing basin, but it may becorrected in accordance with the running results of the coagulantinjection rate in an actual plant. The residence time in a mixing basinis determined depending on the volume of the mixing basin and the amountof water to be treated in an actual plant.

After the coagulant injection rate is computed, the process againreturns back to the sample discharge step, and the above steps arerepeated. In the above description, demonstrated is an example casewhere plural sample tanks are used; however, as so mentionedhereinabove, one sample tank may be used repeatedly for determining theagglomeration start time of water samples each having a differentcoagulant injection rate. In addition, the reasonable coagulantinjection rate computed in the manner as above may be utilized as a setvalue in changing manually the injection rate in an actual plant, or ininputting into the injection rate control system in a central monitorunit.

Next described is a comparative explanatory view of FIG. 8 showing aconventional method and a method of the present invention, relative tothe time to be taken for determination of coagulant injection rate inthose methods. According to the invention, the reasonable coagulantinjection rate may be determined within a shorter period of time, ascompared with the jar test. This is because, as in FIG. 8, the inventiondoes not require the slow mixing step and the statically keeping stepwhich the jar test requires.

Example 2

Next, Example 2 is described with reference to FIGS. 9 to 12. As in FIG.9, the coagulation analyzer in the invention comprises a sample tank 1for keeping a predetermined amount of raw water, water supply/dischargevalves 2, 2E, a mixer 3, a raw water intake valve 4, a raw waterdischarge valve 5, a tap water intake valve 6, a water supply pump 7, afilter 8, a filter inlet valve 9, a raw water feed valve 10, a waterdischarge valve 11, a water level control tank 14 connected to a duct 13through which the overflow from the overflow tube 17 is discharged away,a coagulant 20, a coagulant injection unit 21, a coagulant injectiontube 22, a detector 36 for determining the mean particle size and themean particle number of flocs, a water intake tube 31, a water intakepump 32, a sequencer 34 for analyzing the electric signal 33 fromdetector and for device control, and a POD 35 for displaying measuredvalue and for inputting condition data in device setting.

In this, the detector 36 comprises a light beam radiation unitcomprising any of a laser, LED or lamp for radiating light beams towarda water sample, a photoelectric converter that receives at least any onelight of the front scattering light, the side scattering light, the backscattering light or the transmitted light generated by the particlescontained in a water sample, and converts it into an electric signal,and an electric circuit that determines the mean particle size and themean particle number of flocs from the mean value and the standarddeviation of the converted electric signals. Concrete methods ofdetermining the particle size and the particle number are described inPatent Reference 4. The detector 36 in this Example functions accordingto the above-mentioned fluctuation analyzing method; however, for this,an optical system that functions according to the particle countingmethod described in Patent Reference 3 may also be employed.

Next described is a concrete process of the method for determining theagglomeration start time. First, the basic operation in the process ofthe water sample discharge step, the washing water feed step, the zerowater determination step, the washing water discharge step, the rawwater feed step, and the water level control step is the same as inExample 1. The different points are that the number of the sample tanksis one, which is, however, a plural number in Example 1, that theoverflow wall in the water level control tank is changed to the overflowtube, and that the stage and the injector tube operator for coagulantare omitted.

After the water level control, the mixer 3 is driven at a predeterminedrevolution speed, and then the water intake pump 32 is driven. In thisstep, the discharge water from the water intake pump may be returnedback to the sample tank 1. Next, using an injection rate formula withparameters of the quality such as the turbidity, the alkali degree, thepH and the temperature of the raw water, as determined by thecoagulation analyzer or by any other device, the coagulant injectionratio that is expected to be reasonable is previously found, and this isset as the coagulant injection rate in the sample tank 1. Next, acoagulant 20 is injected into the sample tank 1 from a coagulantinjection unit 21 that comprises a metering pump or a syringe pump(hereinafter this is referred to as a coagulant injection step).

After the coagulant is injected, it is dispersed by mixing to startagglomeration of particles. FIG. 10 shows the profile of the meanparticle size of the flocs measured with the detector 36. In this, themean particle size of the flocs is outputted and led into the sequencer34 via the electric signal 33 from the detector; and the time at whichthe particle size of the flocs begins to increase from the coagulantinjection start time is kept in memory in the sequencer, as a flocgrowth start time. On the other hand, the profile of the mean particlenumber of the flocs is as in FIG. 11, and the time at which the numberof the flocs begins to increase from the coagulant injection start timeis kept in memory as a floc number increase start time (hereinafter thisis referred to as an agglomeration start time determination step).

Either one of the floc growth start time or the floc number increasestart time is taken as the agglomeration start time; or the mean valueof both the two is taken as the agglomeration start time; and this maybe previously determined, and any of these may be employed herein.

In case where the difference between the measured value of theagglomeration start time as determined in the above and the reasonablevalue of the agglomeration start time as previously set in accordancewith a water treatment plant falls within a predetermined range, thenthe coagulant injection rate corresponding to the predetermined amountof the coagulant in the above agglomeration start time determinationstep is determined as a reasonable coagulant injection rate; but in casewhere the difference is larger than the predetermined range, then thereasonable coagulant injection rate is computed according to the processof (21) to (23) in the above-mentioned claim 3. Its details aredescribed below.

Specifically first, the relation between the coagulant injection rateand the agglomeration start time is found as a general formula throughexperiments. Some general formulae may be proposed, but for example,herein employable is the following numerical formula (1) represented byan exponential function:

T=α exp(−βP)  (1)

wherein T represents an agglomeration start time; P represents acoagulant injection rate; α and β are constants that differ depending onthe quality such as the temperature, the pH, the alkali degree and theturbidity of water. Next, from at least one parameter of the quality ofthe raw water with which the agglomeration start time is determined, oneconstant α is defined. The relation between the parameter of the waterquality and α is previously found through experiments.

Next, the numerical value of α, the measured value of the agglomerationstart time and the coagulant injection rate at that time are given tothe general formula, whereby the value of β in the general formula isfound, and thus all the constants in the general formula are therebydetermined (hereinafter this is referred to as an injection ratecomputation formula).

In this, even though the general formula is represented by functionsdiffering from those in the formula (1), the constants may be sodetermined that the number of the unidentified constant in the generalformula is only one on the basis of the relation between the waterquality and the constant obtained through experiments, before themeasured value of the agglomeration start time and the coagulantinjection rate are given to the formula.

Next, the reasonable value of the agglomeration start time is given tothe injection rate computation formula, and the reasonable coagulantinjection rate is computed. The above is a detailed description of thereasonable coagulant injection rate computation step.

FIG. 12 is an example showing the relation between the measured valueand the reasonable value of the agglomeration start time, the generalformula of coagulant injection rate and agglomeration start time, andthe injection ratio computation formula after determination ofconstants. In this drawing, the measured value of the agglomerationstart time is larger than the reasonable value thereof, the coagulantinjection rate is corrected (increased). Specifically, the measuredvalue of the agglomeration start time and the coagulant injection rateat the time are given to the general formula that varies depending onthe water quality, and the injection rate computation formula is therebydetermined. Accordingly, the reasonable value of the coagulant injectionrate may be found so that the agglomeration start time could be thereasonable value thereof. Changing the injection rate in an actual plantto the thus-determined, reasonable injection rate value makes itpossible to correct the coagulant injection rate determined by theinjection rate computation formula.

As described in the above, the method of the invention where theagglomeration start time is determined with the coagulation analyzer andthe coagulant injection rate is thereby controlled in accordance withthe thus-determined time does not require the process from the slowmixing step to the statically keeping step; and according to the methodof the invention, therefore, the coagulant injection rate may beautomatically determined within a shorter period of time as comparedwith any other conventional method.

1. A method of determining the ratio of the amount of coagulant to beinjected to the amount of water to be treated (coagulant injection rate)in a process of water treatment through coagulant injection to water tobe treated followed by coagulation and sedimentation, which comprisesthe following steps: (1) a step of collecting a predetermined sameamount of the water to be treated in every one of plural sample tanks,and then injecting a predetermined different amount of a coagulant toeach water sample collected in those sample tanks, thereby preparingwater samples each having a different coagulant injection rate(coagulant injection step); (2) a step of individually mixing, after thecoagulant injection thereto, every water sample to thereby disperse thecoagulant therein, and individually determining the time taken beforethe start of agglomeration of the particles in each water sample(agglomeration start time) for every water sample (agglomeration starttime determination step); (3) a step of computing, based on theagglomeration start time determined for every water sample and on thecoagulant injection rate for them, the correlation between theagglomeration start time and the coagulant injection rate, as a fittingline (fitting line computing step); (4) a step of computing, based onthe reasonable agglomeration start time data previously set for a watertreatment plant and on the above fitting line, a reasonable coagulantinjection rate for the water treatment plant (reasonable coagulantinjection rate computing step).
 2. The coagulant injection ratedetermination method as claimed in claim 1, which comprises thefollowing (1a), (2a) and (2b) in place of the steps (1) and (2): (1a) astep of collecting a predetermined amount of water to be treated in onesample tank, then injecting a predetermined amount of a coagulant to thewater sample collected in the sample tank, and after the coagulantinjection, dispersing the coagulant by mixing, and determining the timetaken before the start of agglomeration of the particles in the watersample (agglomeration start time); (2a) after the above step, a step ofwashing the sample tank with washing water, then removing the washingwater from the sample tank, then again collecting a predetermined amountof the water to be treated in the sample tank, and injecting apredetermined amount, which differs from that in the above step, of thecoagulant into the water sample, and determining the agglomeration starttime for the water sample; (2 b) a step of repeating the operation ofthe above step plural times with varying the coagulant injection amountevery time, and determining the agglomeration start time for every watersample each having a different coagulant injection rate.
 3. A method ofdetermining the ratio of the amount of coagulant to be injected to theamount of water to be treated (coagulant injection rate) in a process ofwater treatment through coagulant injection to water to be treatedfollowed by coagulation and sedimentation, which comprises the followingsteps: (1) a step of collecting a predetermined amount of the water tobe treated in one sample tank, then injecting a certain amount, which ispredetermined on the basis of the quality of the water to be treated, ofa coagulant to the water sample collected in the sample tank, and afterthe coagulant injection thereto, mixing it to thereby disperse thecoagulant therein, and determining the time taken before the start ofagglomeration of the particles in the water sample (agglomeration starttime); (2) when the difference between the measured value of theagglomeration start time as determined in the above and the reasonablevalue of the agglomeration start time as previously set in accordancewith a water treatment plant falls within a predetermined range, a stepof determining the coagulant injection rate corresponding to thepredetermined amount of the coagulant in the above step (1), as thereasonable coagulant injection rate; but when the above difference islarger than the predetermined range, a step of computing the reasonablecoagulant injection rate according to the following process of (21) to(23): (21) the correlation between the agglomeration start time and thecoagulant injection rate is defined by a general formula including twoconstants, then based on the database previously obtained throughexperiments, one of those constants is defined based on the quality ofthe water to be treated, and the general formula including one constantis found; (22) based on the general formula including one constant andon the measured value of the agglomeration start time and the coagulantinjection rate at that time, the other constant is found, whereby thecomputational formula for the correlation between the agglomerationstart time and the coagulant injection rate is specifically defined;(23) based on the specifically-defined computational formula and thereasonable value of the agglomeration start time as previously set inaccordance with the water treatment plant, the reasonable coagulantinjection rate is computed.
 4. The coagulant injection ratedetermination method as claimed in claim 1, wherein the number of theparticles in the water sample is counted in their respective particlesize sections, and the agglomeration start time is specifically definedby at least any one time of a particle number decrease start time thatis determined for the particles previously existing in the water samplebefore the coagulant injection thereinto and falling in predeterminedsmall particle size sections, or a particle number increase start timethat is determined owing to the start of agglomeration after thecoagulant injection for the particles in the predetermined particle sizesections larger than those in the above predetermined small particlesize sections.
 5. The coagulant injection rate determination method asclaimed in claim 1, wherein the mean particle size and the number of theparticles in a water sample are determined, the time at which the meanparticle size begins to increase is counted as a floc growth start time,and the point at which the mean particle number to be counted as thenumber of flocs begins to increase is defined as a floc number increasestart time, and the agglomeration start time is specifically defined byat least any one time of the floc growth start time or the floc numberincrease start time.
 6. The coagulant injection rate determinationmethod as claimed in claim 1, wherein the reasonable value of theagglomeration start time to be previously set in accordance with a watertreatment plant is one to be set on the basis of the residence time ofthe water to be treated in the mixing basin provided in the watertreatment plant.
 7. An apparatus for carrying out the coagulantinjection rate determination method of claim 1, which comprises at leastone sample tank equipped with a mixer, a coagulant injection device forinjecting a predetermined different amount of a coagulant, anagglomeration start time counter, and a computer device for computing areasonable coagulant injection rate.
 8. The coagulant injection ratedetermination method as claimed in claim 3, wherein the number of theparticles in the water sample is counted in their respective particlesize sections, and the agglomeration start time is specifically definedby at least any one time of a particle number decrease start time thatis determined for the particles previously existing in the water samplebefore the coagulant injection thereinto and falling in predeterminedsmall particle size sections, or a particle number increase start timethat is determined owing to the start of agglomeration after thecoagulant injection for the particles in the predetermined particle sizesections larger than those in the above predetermined small particlesize sections.
 9. The coagulant injection rate determination method asclaimed in claim 3, wherein the mean particle size and the number of theparticles in a water sample are determined, the time at which the meanparticle size begins to increase is counted as a floc growth start time,and the point at which the mean particle number to be counted as thenumber of flocs begins to increase is defined as a floc number increasestart time, and the agglomeration start time is specifically defined byat least any one time of the floc growth start time or the floc numberincrease start time.
 10. The coagulant injection rate determinationmethod as claimed in claim 3, wherein the reasonable value of theagglomeration start time to be previously set in accordance with a watertreatment plant is one to be set on the basis of the residence time ofthe water to be treated in the mixing basin provided in the watertreatment plant.
 11. An apparatus for carrying out the coagulantinjection rate determination method of claim 3, which comprises at leastone sample tank equipped with a mixers a coagulant injection device forinjecting a predetermined different amount of a coagulant, anagglomeration start time counter, and a computer device for computing areasonable coagulant injection rate.